Osteoarthritis (OA) is the most common disease affecting human joints. It is second only to cardiovascular disease as the cause of chronic disability in adults. Worldwide, billions of dollars are spent annually for its treatment and for the lost days in work.
OA is widely considered to be a degenerative joint disease and more than 50% of individuals above the age of 65 years have clinical evidence of OA. Nevertheless, OA cannot be described as a simple consequence of aging. Epidemiological studies have shown a strong correlation of OA with obesity, physical sports and occupation. Moreover, mechanical stress through the joint has been suggested as one of the most important independent etiological factors.
While physiological stress is needed for cartilage and bone sustenance and repair, excessive stress through joint surface leads to initiation and progression of OA. Prolonged high stress and excessive impulsive stress are detrimental to cartilage viability, whereas repetitive physiological stress is beneficial for cartilage health.
Patients with OA generally present with pain, stiffness and deformity of the joint. Present treatment protocols are mainly symptomatic treatment. Initial management of most patients includes changes in lifestyle, Non-Steroidal Anti-Inflammatory Drugs (NSAIDs), analgesics, physical therapy, bracing and ambulatory aids. Surgical treatment is indicated only when consecutive treatment fails to improve the symptoms.
With particular reference to the knee common surgical options include arthroscopic debridement, high tibial osteotomy (HTO), and unicompartmental or tricompartmental knee replacement. In general, present forms of joint replacement surgery completely sacrifice the natural joint and only provide limited symptom relief and restricted mobility. Further, the lifespan of the replaced joint is also limited. None of the presently available treatment methods change the natural progress of the disease.
It is known to provide knee implants. One example of such a device is disclosed in United States Patent Publication No. 2008/0275561 A1 to Exploramed NC4, Inc. The patent discloses various implants used for absorbing energy between body parts, and in particular knee joints.
The implants disclosed in the Exploramed patent are intended to absorb energy when the knee is extended (e.g. the leg is straight). That energy is absorbed by an energy manipulator such as a spring or elastomeric material. The energy is subsequently distributed into the localised knee area on flexion of the knee (e.g. bending of the leg). However, the configurations of the implants of the Exploramed patent only rely on the native knee joint to provide the range of motion for knee movement. That is, the ends of the tibia and femur bones continue to provide articulation of the knee. This limits effectiveness of the disclosed devices as it will affect the natural mechanism of the knee joint such as by creating an unnatural arc of motion.
An implant must also be positioned inside the body e.g. inside or adjacent to a joint. However, the implant may interact with parts of the joint such as the ligaments which hold the bones of the joint together. For instance, an implant could lie overtop of, or otherwise rub, the ligaments, and/or could restrict the ligaments as the joint moves through a native range of motion. This is a particularly difficult issue to address because the ligaments around the knee are complex, and the shape, orientation and direction of these change as the knee flexes. These issues can reduce or limit the effectiveness of the implant(s), or its suitability for use in treating certain conditions.
It is an object of the present invention to provide an improved implant and method of employing same.
It is also an object of the invention to provide an implant which may be more easily implanted to a patient.
It is yet a further object of the invention to provide an implant which may reduce or minimise the adverse effects on the native knee joint when implanted therein.
Yet a further object of the invention is to provide an implant which reduces undesirable interactions with ligaments and muscles forming part of, or adjacent to, a joint.
In addition, it is an object of the present invention to address the foregoing problems or at least to provide the public and medical profession with a useful choice.
In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.
All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.
Throughout this specification, the word “comprise”, or variations thereof such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.